OH/HO2 Instrument

Laser-induced fluorescence instrument for the detection of OH and HO2

LIF is used for detection because of
its sensitivity and selectivity. Tunable UV light is produced by a narrow
bandwidth tunable dye laser pumped by a high repetition rate, solid state
Nd:YAG laser. Ground state OH molecules are promoted to the first
electronically excited state via the Α2Σ+ (ν’ = 1) ← Χ2Π3/2 (ν” = 0) transition at 282 nm. Some
of the vibrationally excited molecules relax to ν’ = 0 via vibrational energy transfer and subsequently
fluoresce near 309 nm. Air flow is introduced to the detection region of the
instrument in a boundary layer free manner using a two-ducted system. OH
radicals are measured by laser induced fluorescence (LIF) at the center of the
sampling duct, avoiding the edges where ambient OH is lost to the walls. HO2
is measured as OH after chemical conversion to OH with nitric oxide via the
reaction: HO2 + NO → OH + NO2.